The system dynamics of the metastatic process from a transplanted fibrosarcoma in mice are being analyzed with and without BCG Therapy. The study is proceeding as follows: (1) Development of mathematical models of the metastatic process for which computer solutions simulate experimental data. (2) Experimental characterization of the dynamics of a weakly immunogenic fibrosarcoma. (3) Experimental characterization of the dynamics of a strongly immunogenic fibrosarcoma. (4) Analysis of the difference in metastatic propensity between these tumor types for most effective BCG immunotherapy. During the first 6 months of this study, several mathematical models have been evaluated and model parameters quantified with respect to the weakly immunogenic tumorhost system. Experimental studies demonstrate that extralesional treatment of the host with BCG does not have a significant effect on the development of pulmonary metastases regardless of tumor development at the time of injection. On the other hand, intralesional BCG treatment does significantly decrease metastases formation, but only when administered very early in the course of tumor development.